The Eternal Jukebox - For when your favorite song just isn't long enough
The Wub Machine - Turn any music into Dubstep, Drum & Bass, and more.
YOU.DJ - Mix SoundCloud music and Youtube videos live in your browser.
Madeon's Adventure Machine - Online remixing tool
itDj - itDJ lets you beat-match, scratch and add effects to your music.
The Beat Machine - The Beat Machine is a webapp for procedurally remixing songs, based on the associated beatmachine Python library